1. Field of the Invention
The present invention pertains to a reciprocating plunger pump power end structure particularly adapted for a pump for pumping liquid nitrogen as well as other cryogenic fluids.
2. Background Art
The increasing use of cryogenic fluids in various applications has presented special problems in the design and application of pumping equipment for such fluids. Liquid nitrogen is one of the more popular cryogenic fluids because of its widespread availability in the earth's atmosphere, its chemical inertness and the relative ease with which it may be liquified. However, certain applications of liquid nitrogen present special problems in the design of pumping equipment.
One increasingly popular use of liquid nitrogen is in connection with enhanced recovery of subterranean petroleum deposits. The injection of nitrogen into geologic formations to stimulate recovery of crude oil, in particular, requires special pumping equipment. Reciprocating plunger type pumps are basically the only suitable type of equipment for handling and pumping liquid nitrogen under the flow rates and working pressures required in petroleum recovery operations. However, the problems associated with maintaining nitrogen in liquid form during certain phases of the pumping process, and the variation in pumping pressures and flow rates required during utilization of the fluid has been particularly difficult to deal with as regards the design of a suitable and reliable pump.
Liquid nitrogen is normally delivered to a well site in an insulated storage tank mounted on a servicing vehicle which also includes the requisite pumping equipment for discharging the nitrogen from the reservoir or storage tank to its end use. The liquid nitrogen must be adequately thermally insulated in the pumping equipment itself to prevent premature evaporation and the resultant erratic and dangerous pump operating conditions. Accordingly, the pump structure must be designed to effectively insulate the working or fluid end of the pump and to also deal with the thermal expansion and contraction caused by the extreme temperatures to which the pump is subjected. The pump fluid end must, of course, be effectively thermally isolated from the power end to prevent unwanted heat generated by mechanical friction in the power end from being transferred to the working fluid.
Moreover, pumping equipment for liquid nitrogen and certain other cryogenic fluids must be designed with good volumetric efficiency to prevent unwanted vaporization of the nitrogen on the suction stroke of the pump plunger. The control over the dimensional relationships necessary for good volumetric efficiency in the pump cylinder combined with the high working pressures and widely varying flow rates experienced by the pumping equipment has presented several problems in regard to the proper design of the power end of high pressure pumps for cryogenic fluids. The design of the power end must be such as to minimize elongation or compression of the pump mechanism so that dimensional control over the pump cylinder and plunger may be maintained for good volumetric efficiency while yet preventing mechanical interference of the working parts due to thermal expansion or contraction. In this regard, the design of a pump for pumping liquid nitrogen also presents a problem because of the relatively high compressibility factor for liquid nitrogen as compared with other liquids. Moreover, the widely varying flow rates required in some applications of pumping liquid nitrogen require special considerations in the design of the crankshaft and connecting rod arrangement, in particular, in regard to bearing loading, bearing configuration and lubrication.
The overall combination of design problems presented by the application of reciprocating plunger pumps to pumping liquid nitrogen and the like have been particularly vexatious for pump designers prior to the development of the present invention.